The paper addresses some of the problems that must be understood and solved before the effects of metal-humic complexation on water treatment processes can be quantitatively addressed. The heterogeniety of ligands in a humic substance not only complicates the mathematical description of equilibrium data but also makes the complexation capacity of a humic substance almost impossible to accurately determine. Complexation capacities (meq/g) of humic substances are widely reported to vary with pH, ionic strength, concentration of the humic substances used in the measurement, and the nature of the metal being studied. The paper demonstrates that the reported effect of humic substance concentration on complexation capacity is an artifact, and that other effects arise from variations in conditional concentration quotients for metal complexation reactions.